1. Field of the Invention
In general, the present device relates to a mutual locking device for electromagnetic contactors applicable to the forward-to-backward operation of a motor. In particular, the present invention relates to a mutual locking device for use in mechanically interlocking two electromagnetic contactors which are reversibly connected in order to prevent the simultaneous closing of the electromagnetic contactors.
2. Discussion of the Related Art
A mutual locking device of the sort shown in FIGS. 6-8 inclusive, is well known. FIG. 6 shows a transverse sectional view of two electromagnetic contactors in an open state. FIG. 7 shows a transverse sectional view of one electromagnetic contactor in a closed state. FIG. 8 shows an exploded perspective view of the two electromagnetic contactors.
In FIG. 6, there are shown two reversibly-connected electromagnetic contactors 1A, 1B, and moving contact supports 2A, 2B for supporting respective moving contacts, the moving contact supports 2A, 2B being vertically movable. A mutual locking device 3 is used for preventing the simultaneous closing of the electromagnetic contactors 1A, 1B. The device is equipped with a pair of driven members 5A, 5B, a locking pin 6 disposed in a V-shaped cavity 18 formed between tilted edge faces 16A, 16B of driven members 5A, 5B and backing members 10A, 10B.
The driven members 5A, 5B are coupled to the respective moving contact supports 2A, 2B via arms 17A, 17B, and driven to when the electromagnetic contactor 1B is closed. When the driven member 5B descends, the locking pin 6 is pushed to the left by the tilted edge face 16B of the driven member 5B and caused to slide onto the underside of the driven member 5A. As a result, the driven member 5A is prevented by the backing member 10A from descending via the locking pin 6 and the electromagnetic contactor 1A is not allowed to close. While the electromagnetic contactor 1A is in the closed state, the electromagnetic contactor 1B is also not allowed to close. In other words, the mutual locking device 3 operates to prevent the simultaneous closing of the electromagnetic contactors 1A, 1B. However, as shown in FIG. 6, when the locking pin 6 is located at the center the descent of either of the driven members 5A, 5B may be obstructed.
FIG. 9 shows a control circuit in a forward-to-backward operating device for a motor using the electromagnetic contactors 1A, 1B. Electromagnetic coils F, R are connected in parallel via a stop push button switch 21. Opened contacts 22A, 22B, which constitute a closing push button switch, and the closed contacts 24B, 24A of the electromagnetic contactors 1B, 1A are inversely connected in series, respectively. When the excitation circuit of the electromagnetic coil F or R on one side is closed, the excitation circuit of the electromagnetic coil R or F on the other side is opened. These excitation circuits are thus electrically interlocked with each other. There are also provided closed contacts 23A, 23B mechanically interlocked with the opened contacts 22B, 22A of the closing push button switch. move in symmetric cases 4A, 4B while being in contact with each other. The cases 4A, 4B are held with positioning projections 9A, 9B fitted into the respective side walls of the electromagnetic contactors 1A, 1B as shown in FIGS. 6-8. A front and a rear reset spring 7 in combination are used to bias the locking pin 6 upward and press it against the tilted edge faces 16A, 16B so that it is located in the center of the cavity 18.
FIG. 8 is an exploded perspective view of parts constituting the mutual locking device 3 above. Windows 8A, 8B, bored in the cases 4A, 4B, are intended for use in passing the respective arms 17A, 17B of the driven members 5A, 5B. At one end, the reset springs 7 are hooked onto the locking pin 6. At the other end, the reset springs 7 are hooked onto the respective abutting ends of cylindrical projections 11A, 11B incorporated within the cases 4A, 4B. The backing members 10A, 10B are prismatic and integrally formed with the cases 4A, 4B. The cases 4A, 48, incorporating the driven members 5A, 5B, the locking pin 6 and the reset springs 7, are set to face each other and fastened together by means of screws 13 that are forced into screw holes 12B through holes 12A.
With this arrangement, when the electromagnetic contactors 1A, 1B are closed with moving cores (not shown) attracted downwardly as shown in FIG. 7, the moving contact supports 2A, 2B, which are integrally connected with the moving cores, are also caused to move and the driven members 5A, 5B descend correspondingly while guided by the inner wall surfaces of the cases 4A, 4B and the mutual contact surfaces 15A, 15B (FIG. 8). FIG. 7 shows the position to which the driven member 5B descends
The conventional device described by reference to FIGS. 6-8 has the following shortcomings:
(1) The mutual locking device 3 has no built-in closed contacts. For this reason, with the provision of the electrical interlocking shown in FIG. 9, the mechanical interlocking requires direct use of only the closed contacts of the electromagnetic contactors 1A, 1B which, in turn, results in a shortage of effective closed contacts. Consequently, the number of closed contacts necessary for the intended circuit may become insufficient. In such a case, some measures have to be taken to separately provide additional auxiliary contacts or relays.
(2) Although it has been arranged so that the locking pin 6 is attracted by the reset springs 7 to the tilted edge faces 16A, 16B of the driven members 5A, 5B to ensure that it is held thereon, the reset springs 7 have to be extended to accommodate the locking pin 6 in the cavity 18 when the mutual locking device 3 is fabricated. Assembly thus becomes difficult and time consuming.